External Timed I/O Semantics Preserving Utilization Optimization for LET-Based Effect Chain

In real-time systems, it is essential to verify the end-to-end constraints that regulate the external input/output (I/O) semantics of the head and tail tasks in each effect chain during the design phase and preserve them during implementation. The logical execution time (LET) model has been adopted by the industry due to the predictability and composability of its timed behavior. However, during the execution of LET-based effect chains, there are ineffective jobs whose outputs are redundant or unused and do not contribute to the external I/O behavior. This letter proposes an offline optimization method for deriving multiframe tasks that achieve the external timed I/O semantics of the LET-based effect chains with reduced utilization. The method first removes ineffective jobs from each effect chain and further explores the benefits of removing jobs for single and crossing effect chains by loosening the LET interval. The method is evaluated using synthetic benchmarks that mimic real-world automotive applications.